Aluminum alloy has been conventionally and widely used as a structural material for aircrafts, spacecrafts, and vehicles due to its characteristic as having a specific gravity lower than that of iron and steel materials. The aluminum alloy, as being the structural material, has been desired to further reduce its weight, and at the same time, the aluminum alloy has been desired to have high strength. For example, Patent Documents 1 to 3 have proposed an aluminum alloy having increased strength.